Inflatable shelter and method of erection

ABSTRACT

A lightweight flexible inflatable shelter for enclosing large areas in applications such as greenhouses, warehouses, recreation areas and other large enclosures, and in various methods of air and water pollution control. The shelter has an envelope of lightweight, low-modulus sheet material such as stretchable fabric or plastic film having high elongation properties. The sheet material is restrained by a cable grid system having heavyduty, longitudinal parallel cables running in one direction and lighter parallel cables running transversely across the longitudinal cables. The cable grid system is tethered to restraint cables or masts at spaced points throughout the structure to restrain the grid system and the sheet material at predetermined elevations from the ground and cause the building, when inflated, to form a plurality of substantially identical dome-shaped roof sections, with the cable grid system and the tether restraint means uniformly distributing stresses throughout the structure. The shelter may be completely assembled on the site by erecting a series of perpendicular masts, draping the cable grid system across the tops of the masts, attaching long strips of sheet material between the rows of draped cables, anchoring the ends of the cables and the sheet material to the ground and inducing internal inflation pressure into the assembled structure.

United States Patent Pierson 1 Feb. 1, 1972 Robert M. Pierson, Hudson, Ohio Envlronmental Structures, Inc., Cleveland, Ohio [22] Filed: Mar. 9, 1970 [21] Appl.No.: 17,675

[72] Inventor:

[73] Assignee:

[52] US. Cl ..52/2, 52/80 [51] Int. Cl ....E04b 1/345 [58] Field otSearch ..52/2, 80

[56] References Cited UNITED STATES PATENTS 2,881,718 4/1959 Stroymeyer ..52/83 X 3,123,085 3/1964 Demarteau ..52/2 3,169,542 2/1965 Neumark ..52/2 3,277,614 10/1966 Marie ..52/2 3,381,424 5/ 1968 Butler ..52/83 3,390,491 7/1968 Hayden et al. ....52/2 X 3,391,504 7/ 1968 McLorg ..52/2 3,496,686 2/1970 Bird ..52/2

FOREIGN PATENTS OR APPLICATIONS 318,700 12/ l 969 Sweden ..52/2 436,677 1 l/ 1967 Switzerland ..52/2

Primary Examiner-Frank L. Abbott Assistant Examiner-Sam D. Burke Attorney-F. W. Brunner and Paul E. Milliken [57] ABSTRACT A lightweight flexible inflatable shelter for enclosing large areas in applications such as greenhouses, warehouses, recreation areas and other large enclosures, and in various methods of air and water pollution control. The shelter has an envelope of lightweight, low-modulus sheet material such as stretchable fabric or plastic film having high elongation properties. The sheet material is restrained by a cable grid system having heavy-duty, longitudinal parallel cables running in one direction and lighter parallel cables running transversely across the longitudinal cables. The cable grid system is tethered to restraint cables or masts at spaced points throughout the structure to restrain the grid system and the sheet material at predetermined elevations from the ground and cause the building, when inflated, to form a plurality of substantially identical dome-shaped root sections, with the cable grid system and the tether restraint means unifonnly distributing stresses throughout the structure. The shelter may be completely assembled on the site by erecting a series of perpendicular masts, draping the cable grid system across the tops of the masts, attaching long strips of sheet material between the rows of draped cables, anchoring the ends of the cables and the sheet material to the ground and inducing internal inflation pressure into the assembled structure.

19 Claims, 11 Drawing Figures PATENTEDFEB H912 SHE! 1 BF 2 IN VENTOR. ROBERT M P/ERSO/V ATTORNEY PATENIED FEB 1 my.

SHEET 2 OF 2 INVENTOR. ROBERT M P/ERSO/V A TTORNE) INFLATABLE SHELTER AND METHOD OF ERECTION This invention relates to a cable-restrained, inflatable shelter for enclosing large areas in applications such as greenhouses, warehouses, recreation areas, pollution control and other large structures.

DESCRIPTION OF THE PRIOR ART The prior art discloses many types of inflatable buildings including those in which flexible, but essentially nonextensible sheet material is reinforced by cables which, in some instances, are restrained by some type of internal tethering within the building to control the overall contour of the building. The closest known prior art to applicant's present invention are U.S. Pat. No. 3,123,085 issued to P. Demarteau, U.S. Pat. No. 3,169,542 to 0. W. Neumark and U.S. Pat. No. 3,391,504 issued to T. W. McLorg. While all these prior patents disclose the concept of an inflatable building with some form of internal tethering, the manner in which applicant uses the cable grid and tethering to distribute the stresses throughout the entire structure provides a new approach to the design and erection of inflatable buildings which has certain advantages over the prior devices which will be described in detail later in the specification.

OBJECT OF THE INVENTION An important object of this invention is to provide a lightweight, inexpensive inflatable structure for covering large areas which may be easily erected at a minimum expense from simple components assembled on site in any desired location and which requires a minimum of skill in erecting the assembly.

Another object of the invention is to provide a shelter which will withstand high wind loads.

Another object of the invention is to provide a shelter which can use sheet material in rolls of uniform width and does not require the cutting of special gores or segments of any particular shape or prefabrication of complex subassemblies prior to shipment to erection site.

Still another object of the invention is to provide an inflatable shelter in which the individual strips of sheet material may be easily removed and replaced without replacing the entire flexible cover of the entire shelter.

A further object of the invention is to provide a shelter which may be erected on uneven terrain and over obstructions such as trees, buildingsand other large objects.

An even further object of the invention is to provide a lowcost shelter of such size that it may enclose large areas in the control of air and water pollution.

These and other objects of the invention will become more fully apparent as the description proceeds in the following specification and the accompanying drawings.

DESCRIPTION OF THE DRAWINGS FIG. I is a diagrammatic perspective view illustrating one of the basic modular units of the shelter;

FIG. 2 is a perspective view showing an inflated shelter containing a group of the modular units shown in FIG. 1;

FIG. 3 is a perspective diagrammatic view showing the building tether point geometry in which the tether points lie in a flat plane;

FIG. 4 is a diagrammatic perspective view similar to FIG. 3 but showing the tether point geometry of a structure having the tether points lying in a cylindrical plane;

FIG. 5 is still another diagrammatic perspective view showing a spherical tether point geometry;

FIG. 6 is a diagrammatic cross-sectional view through a shelter constructed according to the present invention showing the means of adapting the shelter to fit over irregular terram;

FIG. 7 is a perspective view of a shelter in the process of erection;

FIG. 8 is a fragmentary cross-sectional view showing one embodiment of the invention;

FIG. 9 is a fragmentary perspective view showing a connector joining together a main cable and a smaller auxiliary cable;

FIG. 10 is a fragmentary cross-sectional view similar to FIG. 9 but showing a means for clamping the cables within the connector to prevent sliding of the cables with respect to the connector; and

FIG. 11 is a perspective view showing a cable connector with a means for attaching one of the vertical tether cables.

DESCRIPTIONOF THE PREFERRED EMBODIMENTS Referring to FIGS. 1 and 2 of the drawings and in particular to FIG. 2, a completely assembled and inflated building constructed according to the present invention is indicated generally by the numeral 1. The building I is made up of a plurality of individual dome-shaped modules 2, one of which is shown individually in FIG. I. By combining any one of the modules 2 in side-by-side relationship, any size area may be covered, depending upon the number of modules used. As shown in FIG. 2, an assembled building is comprised of a cable grid system indicated generally by the numeral 3, having heavy-duty longitudinal cables 4 which are arranged substantially parallel to each other in a generally horizontal plane and a plurality of auxiliary transverse light-duty cables 5 crossing the longitudinal cables at substantially 90 angles. A plurality of internal restraint members 6 are connected at various equally spaced tether points 7 along the length of the longitudinal cables 4 and are anchored at their opposite end to similarly anchor points 8 along the ground. Part of the internal restraint members 6 may be tether cables or other flexible members and part of the restraint members may be rigid posts or masts, the purpose of which will be described later in the specification.

The term cable" as used herein in describing cables 4, 5 and 6 or any others, is defined as any flexible relatively nonextensible load-carrying member, rope cord, band chain, etc., of steel, rubberized glass, plastic or other material.

An envelope 9 made up of individual strips 10 of extensible stretchable film or fabric is connected to the grid system 3 with all the ends of the cables4 and 5 and of the envelope strips 10 anchored around the periphery of the building 1 in such manner as to form a substantiallyairtight structure which may be inflated by inducing internal pressure into the building. The envelope 9 will be described in more detail later in the specification. When the building is inflated, the grid system 3 will determine the shape of and restrain the envelope 9 and cause it to form a plurality of the dome-shaped modules 2 as previously described. Since the means of anchoring the cables and the envelope material do not form a part of this invention, they ,will not be described in detail. It will be assumed, however, that any number of prior art anchoring means may be employed to anchor any of the building structures where it is needed. The building I may be equipped with inflation means such as blowers ll, shown in FIG. 2, and one or more access doors, such as the door 12 mounted in a frame 13 attached to the envelope 9. Although the descriptions have been based on anchoring the cable grid system to the ground at the periphery, as well as sealing the envelope at ground level, many actual situations may require conventionally constructed, rigid walls to form part or all of the periphery. The basic design and mathematics of this invention are unaffected by whether the cables and envelope terminate at ground level or at the top of such a wall.

CABLE GRID SYSTEM As may be seen in FIG. 2, the lightweight auxiliary cables 5 of the grid system 3 are positioned much closer together than the heavy-duty longitudinal cables 4. By positioning the auxiliary cables 5 closer together, this permits a better load distribution from the envelope 9 and improves the restraint characteristics of the overall grid system 3. Moreover, the dual-size cable system is much less costly than for a grid system of cables of identical size in both directions, having similar load capacity.

In designing the cable grid system 3, the cable tensions and anchoring forces are dependent upon the size and shape of the basic tethered module 2 and are directly proportional to the inflation pressure. Longitudinal and transverse cable tensions are readily calculable since the cable shape in each direction approaches that of a circular arc.

The tension, T in the heavy-duty longitudinal cables 4 is found from the following equation:

where C distance between longitudinal cables in feet P= inflation pressure, lbs./sq. ft.

R radius of curvature of the longitudinal cable, in feet The tension in the internal restraint members 6, T,, is found to be:

where C, longitudinal distance between internal restraint members 6, in feet Considering the closely spaced, light-duty transverse cables 5, the cable tensions and anchoring forces are dependent upon the spacing between the transverse cables 5, the size and shape of the basic tethered module 2, and are directly proportional to the inflation pressure.

The transverse cable tension, 7",, is found to be:

TFCIPRI where C, distance between transverse cables, in feet R radius of curvature of each transverse cable, in feet The most economical overall use of cable will be dependent on the ratio of spacing between the parallel lightweight cables in one direction, and the spacing between the parallel heavy cables in the transverse direction. Since this ratio will in most cases be much less than one-half, the size relationship of the main cables to the lighter cables (which need not be of the same material) will in all practical instances be such that the ratio of tensile strengths will be at least four to one.

In the analysis of the transverse cable tensions, the flexible low-modulus envelope material is assumed to carry none of the tension between the longitudinal cables 4.

It is obvious from the equations that increasing the radius of curvature increases the cable requirements. On the other hand, when the radius of curvature is reduced, the elongation requirements imposed on the envelope film material 9 become very great, especially at the tethering points 7. It is necessary to find a compatible radius of curvature which will satisfy both the film properties and the cable specifications.

The possibilities for the overall geometrical shape or locus of points on which the tether points 7 can lie is detennined by analyzing all of the structural components under ideal equilibrium conditions. Module equilibrium requires identically shaped, symmetrically oriented modules with cable and envelope tensions in equilibrium within and between modules. Therefore, it follows that all tether points 7 must be evenly and continuously spaced in each cable direction, and must be symmetrically oriented with respect to the center line of the building. A study of the possible geometric shapes on which the tether points can lie and still fulfill all equilibrium conditions yields that only a plane or a pure cylindrical shape is ideal.

In the case of a plane, as shown in FIG. 3, where the module tether points 7 form a flat roof or ceiling, all equilibrium conditions are fulfilled in the top of the building. Even with this ideal case, special design is required in the comers where the modules are continued to the ground to form the sides of the building. Because the flat roof shape fulfills equilibrium conditions and is the most practical building to design and construct, it is considered the simplest and most practical of all geometric shapes for tether points.

Another ideal but less practical tether point geometry is that of a pure cylindrical element as shown in FIG. 4. The basic drawback to using this shape is that continuous equilibrium conditions are upset when an attempt is made to provide ends on the building. Solid walls are a solution for the ends, but add greatly to the other relatively low cost of a pure grid-envelope structure. To provide ends for a cylindrical building by continuing the cable grid concept, it is necessary to add different tether point geometries at the ends which destroys continuous equilibrium requirements.

The final shape to be considered for possible overall tether point shaping is that of the spherical element shown in FIG. 5.

This shape is not ideal and has practical limitations because i the basic module element cannot be identically repeated on a spherical surface and therefore total equilibrium cannot be achieved.

ENVELOPE DESIGN The envelope 9 or pressurized shell of the inflated structure has been defined as an extensible, stretchable impervious fabric or film, or a combination of the two which is impermeable to air and which restrains internal inflation pressure. The ability of the envelope 9 to stretch in at least one direction is basic to the concept. Module size and shape and the internal pressure determine envelope stresses and elongation requirements. The two cable grid system 3 permits the envelope 9 to stretch in the direction of longitudinal cables 4 while the lightduty transverse cables 5 restrain the envelope 9 from stretching in the transverse direction. The stress per unit width, s, in pounds per foot in the longitudinal direction of the envelope, where the envelope 9 must stretch to meet the longitudinal restraining cables 4, is found to be:

S----PR where P= inflation pressure in Ibs./ft.

R,= radius of curvature of the envelope film in the longitudinal direction, in feet The stress in the transverse direction depends upon the method of construction used and the distance between the transverse cables 5 and is calculable for any particular case. Two-way stretch methods of construction are feasible, but will put increased demands on the envelope material. Special reinforcing of highly stressed areas may be required.

In the selection of an envelope for a particular building, the following material properties should be considered: trapezoidal tear strength, tensile strength, elongation, impact strength, variation of properties due to changing temperature, weight, ease of handling, porosity, insulating properties, color, ultraviolet resistance, soil corrosion resistance, dirt resistance, and hardware abrasion resistance. Fire retardance is also important, although it has been found that inflation pressure serves to rapidly extinguish any flame in the envelope.

The envelope 9 can be prefabricated to cover a portion of a module or one or more entire modules, or, preferably, it can be entirely field fabricated at the building site. Various methods of fastening the envelope seams are possible, including lacing, zippering, heat sealing, cementing, mechanical clamping, taping, or any combination of these and other methods. One effective method of fastening the envelope strips 10 to the cables 5 is described in applicants previously filed copending application, Ser. No. 850,826.

BUILDING STABILITY The buildings stability in winds, especially gusty winds, is dependent upon the ability of its components to rapidly achieve and maintain equilibrium and to readapt quickly to external unbalancing forces. The basic requirements for stability of the simple designs shown are:

I. All longitudinal cables 4 should be evenly spaced.

2. All transverse cables 5 should be evenly spaced.

3. All tethering points 7 should be evenly spaced along the longitudinal cables, and also should be evenly spaced in the transverse direction.

4. The tethering points 7 should fall on the surface of some continuous geometrical shape which is either a plane or a pure cylinder for ideal equilibrium conditions. Other shapes or combinations of shapes are possible, but these depart from the simple ideal case and require special engineering.

5. In a particular direction, all cables should have a constant radius of curvature between tether points throughout the entire length of each cable.

6. Film radius of curvature in either direction should be constant.

7. The film must elongate in at least one direction to permit shaping, bidirectional elongation is preferred.

8. The film should elongate in the same ratio in any given path throughout the building for ideal conditions.

The preceding requirements indicate that a building should preferably be constructed with identically shaped modules which are formed by evenly distributed, symmetrically oriented tethering points. The principal exception to the identically shaped module condition is at the sides of the building as shown in FIG. 6, where the last module can be extended or shortened in one direction to meet the ground where it can be anchored without affecting equilibrium. This inherent characteristic of the structure makes it readily adaptable for covering uneven terrain. As may be seer: in FIG. 6, the building 1 may be erected on uneven terrain by varying the lengths of the cables 6 to compensate for variations in ground level and cause the tether points to lie in a horizontal plane. An important condition for stability here is that the inclination angle a which the side of the structure makes with a horizontal plane is at all times less than 90.

The necessity for limiting the inclination angle to less than 90 comes from wind loading considerations. The ability of the structure to maintain stability under aerodynamic loading is dependent upon inflation pressure which shapes and pretensions the envelope 9 and cable grid system 3. It has been found that for conventional single module ground-mounted structures biased on nonstretchable fabric, the minimum inflation pressure for aerodynamic stability is 50 percent of the dynamic impact pressure of the wind velocity. The minimum design velocity recommended for air supported structures is 60 mph. For this condition, a calculated design inflation pressure of 0.88 inches of water (50 percent of the dynamic impact pressure) would be required for stability. A built-in defense against winds is inherent in enclosures with distendable envelopes, and derives from the slight change in internal volume that accompanies variations in the internal pressure. The normal range of 1.5 to 7 lbs. per square foot corresponds, for most enclosure shapes, to a volume change in the range of 0.5-1.0 percent, neglecting changes contributed by slight lengthening of the cables. Thus, wind pressures exerted on one side produce local decreases in the inside-to-outside pressure differential, decreasing the strain in the distended envelope. The resultant slight contractions in volume of the stretched envelope in turn operate to increase internal pressure, thus offsetting the local decreases on the windward side. Accordingly, properly designed stretchable envelope enclosures, equipped with vents which can release air to relieve local overpressures on the lee side, show better stability in high winds than nondistendable fabric-based enclosures of similar geometries. It is evident from the foregoing, that the physical properties of the envelope material, particularly its stress-strain properties, play a key role both in overall design and in wind performance of the enclosure, and therefore in the selection of the size of components as they affect cost. Two basic features already mentioned concerning the enclosures of this invention, as distinct from air supported buildings based on essentially nonextensible fabric, are (l) the capability of assembling envelope contours of complex double curvature, especially at tiedown points and corners, without the necessity of special cutting or reshaping the initially flat film envelope material (conventional fabric buildings are extensively pretailored to final shape in off-site manufacturing facilities); (2) the expansibility by a significant amount of the overall enclosure volume as inflation pressure operates from the lower to the upper end of its normal operating range, in a fashion somewhat analogous to that of a rubber balloon (conventional fabric buildings undergo very little additional expansion between the lower and upper end of their normal operating pressures, due to the virtual nonextensibility of the fabric used). These features require an envelope material of high ultimate elongation, preferably over 25 percent, and low-extension modulus, preferably below ll pounds per lineal inch of width at l0 percent elongation.

Because of the high local strains that can be imposed on the envelope film material as the enclosure adapts to varying shapes under gusting wind conditions, experience has demonstrated that film materials more nearly approximating the properties of a semifiexible rubber than those of a rigid plastic have been preferable. For example, films of plasticized poly vinyl chloride containing at least 20 percent plasticizer, polyurethane rubber and flexible acrylic ester copolymers containing at least 60 percent 2 ethyl hexyl acrylate, each having ultimate elongations over 200 percent, have satisfied the requirements of high elongation and low modulus better than have films of low elongation, such as Mylar.

In as much as, under conditions of high or gusty winds, the difference between internal and external pressure will vary considerably between different points on the envelope surface, and will fluctuate from one moment to the next, it is highly important that the elasticity of the envelope surface make it possible to accommodate rapidly to local changes in the pressure difference, without gross distortions in module shape. These rapid adaptions are only possible if the film material has stress-strain characteristics which enable its elongation to change rapidly and to a considerable degree. By appropriate design and with use of relatively low ratios of height to span, it is possible to reduce to quite low values the equivalent flat surface wind load to be resisted by internal pressure.

METHOD OF ERECTION The method of erecting a building of the type shown in FIG. 2 is best illustrated in FIG. 7. A plurality of vertical rigid masts 14 are positioned in rows and suitably anchored to the ground. The tops of each row of masts 14 are connected together by the heavy-duty longitudinal cables 4. The transverse lightweight cables 5 are then draped across the longitudinal cables 4 and the ends of all the cables are anchored to the ground around the periphery of the area to be covered by the building. After the transverse cables 5 are in place and suitably anchored, strips 10 of the envelope material may be draped over the longitudinal cables 4 with each of the strips 10 lying between a pair of cables 5. The strips 10 are then fastened to each other and to the cable 5 adjacent totheir edges to form an airtight seam along each of the cables 5. As shown in FIG. 7, the strips 10 are being unrolled from a roll 15 of plastic material of uniform width. This permits easy onsite erection without the need for cutting the envelope material into special shapes or sizes. The strips 10 are simply rolled out to the desired length and cut off. To complete the building shown in FIG. 7, the remaining transverse cables 5 will be added and a strip 10 of envelope material will be fastened between each adjacent pair of cables 5. Once the cable grid system 3 is completely assembled and covered by a complete envelope 9, the building 1 is inflated at a low pressure to cause the envelope to approach its final inflated contour. At this point, the various restraint cables 6 are adjusted in length and the edges of the strips 10 are adjusted to minimize wrinkles and excessive local strain in the envelope material. The internal pressure of the building 1 may preferably be alternately increased and decreased a number of times while the tension adjustment of cables and envelope material are made. For the purpose of simplicity in describing the erection of this enclosure, no mention has been made of the positioning in the walls of doors l2 and other openings and for the installation of blowers 11 and other auxiliary equipment normally used with a building of this type. It will be understood that the installation of such accessories to the enclosure will be carried on in conjunction with the erection of the enclosure.

To further discuss the tether restraint members, either the restraint cables 6 shown in FIGS. 1 and 2 or the rigid masts 14 shown in FIG. 7 may be used as restraint means for the grid system 3. FIG. 8 shows the use of a combination of both rigid masts l4 and flexible restraint cables 6 attached to one of the heavy-duty longitudinal cables 4 at various tether points 7 which lie in a substantially horizontal plane.

As shown in FIG. 9, the cables 4 and may be slidably connected together by a connector 16 comprised of a pair of cylindrical sleeve members 17 and 18 which conform in size to the diameter of the cables 4 and 5.

ln H6. 10, a similar connector 19 is shown in which sleeves 20 and 21 equipped with a pair of clamp jaws 22 and 23 may be tightened against the cables 4 and 5 by tightening bolts 24 and 25 respectively to force the jaws 22 and 23 against the cables and thereby prevent the cables from sliding longitudinally with respect to the connector 19.

FIG. 1 1 shows a connector 26 which is substantially identical to the connector 16 in FIG. 9 but which is fitted with a downwardly extending eyelet 27 to receive the looped end of one of the tether cables 6. The connector fittings shown in FIGS. 9 through 11 are merely one example of a manner of connecting together the various cables in the grid system 3 and the tether restraint cables 6. Various other means may be used without departing from the scope of the invention. It should be realized that so long as the basic grid system described herein it utilized in combination with the extensible envelope material, many variations may be made in the overall building configuration, including the number of modules, the pattern formed by the tether points, and the type of additional accessories used with the building.

As pointed out earlier, the envelope film and cables defining the exterior contour of the enclosure can also terminate at a peripheral wall around either the entire, or a portion of the periphery, as well as to the ground.

Enclosures of this invention, because of their exceptionally low cost, will find many applications related to pollution control and to improving quality of inhabited environments. Uses for controlling pollution will tend to be less than acres in size and not inhabited, and will contain the pollution and trap it in some way to prevent its going outside. Such uses would include rubbish disposal dumps, where the dust and odors attending such operations are filtered out; settling ponds for sewage plants; manufacturing facilities that are sources of noxious eflluvia. inhabited enclosures providing controlled environment for those inside will be able to provide clean air at minimum cost by virtue of the ease with which all incoming air can be washed and filtered, and by requiring that major sources of objectionable gases or particulate matter within the enclosure be required to vent directly outside the enclosure, rather than be released inside.

What is claimed is:

1. An inflatable enclosure having its lower peripheral edges attached to a base, the enclosure comprising:

A. a reinforcing grid having:

1. a plurality of flexible, inextensible, main reinforcing members substantially parallel to each other and to a first opposed pair of peripheraledges of the enclosure.

2. a plurality of flexible, inextensible, auxiliary reinforcing members extending transversely across the main reinforcing members, said auxiliary members being substantially parallel to each other and to a second opposedpajrgf perifleralgdges of the enclosure,

. said main reinforcing members and auxiliary reinforcing members being attached to each other at their points of intersection, and

4. means anchoring the opposite ends of the main and auxiliary reinforcing members to the base at the periphery of the enclosure;

B. tether means connected to spaced locations along the main reinforcing members and to similar spaced locations on the base aligned substantially parallel to the peripheral edges of the enclosure to hold the main reinforcing members at a predetermined distance from the base when the enclosure is inflated; C. a cover envelope comprising: I

l. elongated strips of flexible extensible sheet material of substantially uniform width throughout the length of each strip thereof, attached between the auxiliary reinforcing members to completely cover the entire area embraced by the enclosure,

2. the adjacent marginal side edges of each adjacent strip of sheet material being connected to an auxiliary reinforcing member common to both adjacent edges, the connection forming an airtight seam between the adjacent edges,

3. the ends of the strips of sheet material being anchored in sealing engagement with the base around the outer periphery of the enclosure;

D. means supplying internal inflation pressure to the interior of the shelter in excess of atmospheric pressure; and

E. the relative positions of the tether means with respect to the peripheral edges of the enclosure and the reinforcing members of the grid causing the envelope when inflated to confonn to the shape of a plurality of dome shaped modules.

2. An inflatable enclosure as claimed in claim 1 wherein at least part of the tether means is a plurality of vertical rigid masts.

3. An inflatable enclosure as claimed in claim 1 wherein the main reinforcing members and the auxiliary reinforcing members are slidably attached to each other at the point where they intersect each other.

4. An inflatable enclosure as claimed in claim 1 wherein the main reinforcing members and the auxiliary reinforcing members are fixedly attached to each other at the point where they intersect each other.

5. An inflatable enclosure as claimed in claim 1 wherein the points of connection between the tether means and the main reinforcing members lie in a flat plane.

6. An inflatable enclosure as claimed in claim 1 wherein the points of connection between the tether means and the main reinforcing members lie in a curved plane.

7. An inflatable enclosure as claimed in claim 1 wherein the cover envelope is made of an extensible, low-modulus plastic material with high elongation properties.

8. An inflatable enclosure as claimed in claim 1 wherein the envelope is extensible to an elongation of at least 25 percent.

9. An inflatable enclosure as claimed in claim 1 wherein the main reinforcing members are at least four times the tensile strength of the auxiliary reinforcing members.

10. An inflatable enclosure having its lower peripheral edges attached to a base, the enclosure comprising:

A. a reinforcing grid having:

1. a first set of flexible, inextensible, reinforcing members substantially parallel to a first opposed pair of peripheral edges of the enclosure,

2. a second set of flexible, inextensible, reinforcing members extending transversely across the first set of reinforcing members to form intersections therewith, the members of said second set being substantially parallel to each other and to a second opposed pair of peripheral edges of the enclosure,

. said first set of reinforcing members and said second set of reinforcing members being attached to each other at their points of intersection, and

4. means anchoring the opposite ends of all the reinforcing members to the base at the periphery of the enclosure;

B. tether restraint means connected to spaced locations along the reinforcing members and to similar spaced locations on the base aligned substantially parallel to the peripheral edges of the enclosure to hold the reinforcing members at a predetermined distance from the base when the enclosure is inflated;

C. a cover envelope comprising:

l. elongated strips of flexible extensible sheet material of substantially uniform width throughout the length of each strip thereof, attached to the reinforcing members to completely cover the entire area embraced by the enclosure,

2. the adjacent marginal edges of each adjacent strip of sheet material being connected together to form an airtight seam,

3. the ends of the strips of sheet material being anchored in sealing engagement with the base around the outer periphery of the enclosures; and

D. means supplying internal inflation pressure to the interior of the envelope in excess of atmospheric pressure;

E. the relative positions of the tether means with respect to the peripheral edges of the enclosure and the reinforcing members of the grid causing the envelope when inflated to conform to the shape of a plurality of domed modules; and

F. the extensible sheet material of the envelope stretching at least in some parts thereof upon inflation of the envelope to adjust the envelope dimensions to the dimensions of the reinforcing grid.

11. An inflatable enclosure as claimed in claim 10 wherein at least part of the tether restraint means is a plurality of vertical rigid masts.

12. An inflatable enclosure as claimed in claim 10 wherein the first and second set of reinforcing members are slidably attached to each other at the point where they intersect each other.

13. An inflatable enclosure as claimed in claim 10 wherein the reinforcing members of the grid are fixedly attached to each other at the point where they intersect each other.

14. An inflatable enclosure as claimed in claim 10 wherein the points of connection between the tether restraint means and the reinforcing members lie in a flat plane.

15. An inflatable enclosure as claimed in claim 10 wherein the points of connection between the tether restraint means and the reinforcing members lie in a curved plane.

16. An inflatable enclosure as claimed in claim 10 wherein the cover envelope is made of an extensible, low-modulus plastic material with high elongation properties.

17. An inflatable enclosure as claimed in claim 10 wherein the envelope is extensible to an elongation of at least 25 percent.

18. An inflatable enclosure as claimed in claim 10 wherein the reinforcing members of one set have at least four times the tensile strength of the reinforcing members of the other set.

19. An inflatable enclosure having its lower peripheral edges attached to a base, the enclosure comprising:

A. a reinforcing grid having:

I. at least one flexible, inextensible main reinforcing member substantially parallel to a first opposed pair of peripheral edges of the enclosure,

2. a plurality of flexible, inextensible substantially parallel auxiliary reinforcing members extending transversely across each main reinforcing member and lying substantially parallel to a second pair of peripheral edges of the enclosure,

3. said auxiliary reinforcing members being attached to each main reinforcing member at their points of intersection, and

4. means anchoring the opposite ends of the main and auxiliary reinforcing members to the base at the periphery of the enclosure;

B. tether means connected to spaced locations along each main reinforcing member and to similar spaced locations on the base aligned substantially parallel to the first opposed pair of peripheral edges of the enclosure to hold each main reinforcing member at a predetermined distance from the base when the enclosure is inflated;

C. a cover envelope comprising:

1. elongated strips of flexible extensible sheet material attached to the auxiliary reinforcing members to completely cover the entire area embraced by the enclosure,

2. the adjacent marginal edges of each adjacent strip of sheet material being connected together to form an airtight seam,

3. the ends of the strips of sheet material being anchored in sealing engagement with the base around the outer periphery of the enclosure; and

D. means supplying internal inflation pressure to the interior of the envelope in excess of atmospheric pressure; and E. the relative positions of the tether means with respect to the peripheral edges of the enclosure and the reinforcing members of the grid causing the envelope when inflated to conform to the shape of a plurality of dome shaped modules. 

1. An inflatable enclosure having its lower peripheral edges attached to a base, the enclosure comprising: A. a reinforcing grid having:
 1. a plurality of flexible, inextensible, main reinforcing members substantially parallel to each other and to a first opposed pair of peripheral edges of the enclosure.
 2. a plurality of flexible, inextensible, auxiliary reinforcing members extending transversely across the main reinforcing members, said auxiliary members being substantially parallel to each other and to a second opposed pair of peripheral edges of the enclosure,
 3. said main reinforcing members and auxiliary reinforcing members being attached to each other at their points of intersection, and
 4. means anchoring the opposite ends of the main and auxiliary reinforcing members to the base at the periphery of the enclosure; B. tether means connected to spaced locations along the main reinforcing members and to similar spaced locations on the base aligned substantially parallel to the peripheral edges of the enclosure to hold the main reinforcing members at a predetermined distance from the base when the enclosure is inflated; C. a cover envelope comprising:
 1. elongated strips of flexible extensible sheet material of substantially uniform width throughout the length of each strip thereof, attached between the auxiliary reinforcing members to completely cover the entire area embraced by the enclosure,
 2. the adjacent marginal side edges of each adjacent strip of sheet material being connected to an auxiliary reinforcing member common to both adjacent edges, the connection forming an airtight seam between the adjacent edges,
 3. the ends of the strips of sheet material being anchored in sealing engagement with the base around the outer periphery of the enclosure; D. means supplying internal inflation pressure to the interior of the shelter in excess of atmospheric pressure; and E. the relative positions of the tether means with respect to the peripheral edges of the enclosure and the reinforcing members of the grid causing the envelope when inflated to conform to the shape of a plurality of dome shaped moduLes.
 2. the adjacent marginal edges of each adjacent strip of sheet material being connected together to form an airtight seam,
 2. a second set of flexible, inextensible, reinforcing members extending transversely across the first set of reinforcing members to form intersections therewith, the members of said second set being substantially parallel to each other and to a second opposed pair of peripheral edges of the enclosure,
 2. a plurality of flexible, inextensible, auxiliary reinforcing members extending transversely across the main reinforcing members, said auxiliary members being substantially parallel to each other and to a second opposed pair of peripheral edges of the enclosure,
 2. An inflatable enclosure as claimed in claim 1 wherein at least part of the tether means is a plurality of vertical rigid masts.
 2. the adjacent marginal side edges of each adjacent strip of sheet material being connected to an auxiliary reinforcing member common to both adjacent edges, the connection forming an airtight seam between the adjacent edges,
 2. a plurality of flexible, inextensible substantially parallel auxiliary reinforcing members extending transversely across each main reinforcing member and lying substantially parallel to a second pair of peripheral edges of the enclosure,
 2. the adjacent marginal edges of each adjacent strip of sheet material being connected together to form an airtight seam,
 3. said auxiliary reinforcing members being attached to each main reinforcing member at their points of intersection, and
 3. the ends of the strips of sheet material being anchored in sealing engagement with the base around the outer periphery of the enclosures; and D. means supplying internal inflation pressure to the interior of the envelope in excess of atmospheric pressure; E. the relative positions of the tether means with respect to the peripheral edges of the enclosure and the reinforcing members of the grid causing the envelope when inflated to conform to the shape of a plurality of domed modules; and F. the extensible sheet material of the envelope stretching at least in some parts thereof upon inflation of the envelope to adjust the envelope dimensions to the dimensions of the reinforcing grid.
 3. the ends of the strips of sheet material being anchored in sealing engagement with the base around the outer periphery of the enclosure; D. means supplying internal inflation pressure to the interior of the shelter in excess of atmospheric pressure; and E. the relative positions of the tether means with respect to the peripheral edges of the enclosure and the reinforcing members of the grid causing the envelope when inflated to conform to the shape of a plurality of dome shaped moduLes.
 3. said first set of reinforcing members and said second set of reinforcing members being attached to each other at their points of intersection, and
 3. the ends of the strips of sheet material being anchored in sealing engagement with the base around the outer periphery of the enclosure; and D. means supplying internal inflation pressure to the interior of the envelope in excess of atmospheric pressure; and E. the relative positions of the tether means with respect to the peripheral edges of the enclosure and the reinforcing members of the grid causing the envelope when inflated to conform to the shape of a plurality of dome shaped modules.
 3. An inflatable enclosure as claimed in claim 1 wherein the main reinforcing members and the auxiliary reinforcing members are slidably attached to each other at the point where they intersect each other.
 3. said main reinforcing members and auxiliary reinforcing members being attached to each other at their points of intersection, and
 4. means anchoring the opposite ends of the main and auxiliary reinforcing members to the base at the periphery of the enclosure; B. tether means connected to spaced locations along the main reinforcing members and to similar spaced locations on the base aligned substantially parallel to the peripheral edges of the enclosure to hold the main reinforcing members at a predetermined distance from the base when the enclosure is inflated; C. a cover envelope comprising:
 4. An inflatable enclosure as claimed in claim 1 wherein the main reinforcing members and the auxiliary reinforcing members are fixedly attached to each other at the point where they intersect each other.
 4. means anchoring the opposite ends of all the reinforcing members to the base at the periphery of the enclosure; B. tether restraint means connected to spaced locations along the reinforcing members and to similar spaced locations on the base aligned substantially parallel to the peripheral edges of the enclosure to hold the reinforcing members at a predetermined distance from the base when the enclosure is inflated; C. a cover envelope comprising:
 4. means anchoring the opposite ends of the main and auxiliary reinforcing members to the base at the periphery of the enclosure; B. tether means connected to spaced locations along each main reinforcing member and to similar spaced locations on the base aligned substantially parallel to the first opposed pair of peripheral edges of the enclosure to hold each main reinforcing member at a predetermined distance from the base when the enclosure is inflated; C. a cover envelope comprising:
 5. An inflatable enclosure as claimed in claim 1 wherein the points of connection between the tether means and the main reinforcing members lie in a flat plane.
 6. An inflatable enclosure as claimed in claim 1 wherein the points of connection between the tether means and the main reinforcing members lie in a curved plane.
 7. An inflatable enclosure as claimed in claim 1 wherein the cover envelope is made of an extensible, low-modulus plastic material with high elongation properties.
 8. An inflatable enclosure as claimed in claim 1 wherein the envelope is extensible to an elongation of at least 25 percent.
 9. An inflatable enclosure as claimed in claim 1 wherein the main reinforcing members are at least four times the tensile strength of the auxiliary reinforcing members.
 10. An inflatable enclosure having its lower peripheral edges attached to a base, the enclosure comprising: A. a reinforcing grid having:
 11. An inflatable enclosure as claimed in claim 10 wherein at least part of the tether restraint means is a plurality of vertical rigid masts.
 12. An inflatable enclosure as claimed in claim 10 wherein the first and second set of reinforcing members are slidably attached to each other at the point where they intersect each other.
 13. An inflatable enclosure as claimed in claim 10 wherein the reinforcing members of the grid are fixedly attached to each other at the point where they intersect each other.
 14. An inflatable enclosure as claimed in claim 10 wherein the points of connection between the tether restraint means and the reinforcing members lie in a flat plane.
 15. An inflatable enclosure as claimed in claim 10 wherein the points of connection between the tether restraint means and the reinforcing members lie in a curved plane.
 16. An inflatable enclosure as claimed in claim 10 wherein the cover envelope is made of an extensible, low-modulus plastic material with high elongation properties.
 17. An inflatable enclosure as claimed in claim 10 wherein the envelope is extensible to an elongation of at least 25 percent.
 18. An inflatable enclosure as claimed in claim 10 wherein the reinforcing members of one set have at least four times the tensile strength of the reinforcing members of the other set.
 19. An inflatable enclosure having its lower peripheral edges attached to a base, the enclosure comprising: A. a reinforcing grid having: 